The present disclosure relates to an optically-transparent optical sheet capable of suppressing a deformation due to a thermal expansion, a method of producing the optical sheet, and a surface-emitting apparatus and a liquid crystal display apparatus that include the optical sheet.
A liquid crystal display apparatus includes a liquid crystal display panel and a backlight as an illumination light source. Incorporated into the backlight in addition to a sheet that diffuses light emitted from a light source and a sheet that collects light on the liquid crystal display panel side are various optical sheets such as a polarization separation sheet.
In recent years, along with a prominent progress of thinning of liquid crystal display apparatuses, thinning of optical sheets to be incorporated into backlights of the liquid crystal display apparatuses is under way. One of the problems caused by the thinning of optical sheets is lowering of rigidity. As a rigidity of an optical sheet becomes lower, the optical sheet is more easily deformed by a temperature rise in the backlight. If a linear expansion coefficient of the optical sheet large, a swell is caused in the sheet along with the temperature rise in the backlight, and luminance unevenness due to the swell is visually recognized via a panel.
For solving such a problem, Japanese Patent Application Laid-open No. 2009-21037 (paragraph [0054], FIGS. 1 and 2; hereinafter, referred to as Patent Document 1), for example, discloses a structure in which linear members that restrict a deformation of an optical sheet due to a thermal expansion are provided in a case portion of a backlight. With this structure, the optical sheet and a liquid crystal display panel are prevented from coming into contact with each other, and luminance uniformity of a display screen is secured.
In the structure disclosed in Patent Document 1, however, there is a problem that, since additional components called linear members are required, the number of components of the backlight increases. Moreover, since the linear members are provided across a light-emitting surface of the optical sheet, various restrictions need to be placed on structures and arrangements of the linear members so that the linear members cannot be visually recognized through the panel.
In view of the circumstances as described above, there is a need for an optical sheet capable of suppressing a deformation due to a thermal expansion, a method of producing the optical sheet, and a surface-emitting apparatus and a liquid crystal display apparatus that include the optical sheet.